Japanese Patent Laying-Open No. 2006-118496 discloses a conventional cross-flow fan designed with an attempt to reduce noises caused by fluid oscillation and to improve an air-blow performance (PTL 1). The cross-flow fan disclosed in PTL 1 is provided with at least 34 blades to at most 36 blades. The blades respectively have random pitches (angles), and the following relationship is met; 1.0 (deg)≦Pmax−Pmin ≦2.5 (deg), where Pmax is the largest pitch and Pmin is the smallest pitch.
Japanese Patent Laying-Open No. 2003-269363 discloses a tangential fan blade wheel designed with an attempt to effectively reduce discrete frequency noises (PTL 2). According to the tangential fan blade wheel disclosed in PTL 2, plural blades are divided into even-numbered groups having an equal number of blades. The tangential fan blade wheel is configured to have a pitch difference angle ε meeting the relationship of β=α+γ and γ+α−ε, where α is a virtual average pitch angle, β is a pitch angle between the blades in one of the adjacent groups, and γ is a pitch angle between the blades in the other group. The tangential fan blade wheel is structurally characterized in that respective blocks of the blade wheel are axially displaced by an angle δ and joined with one another to minimize the synthesized sound pressure of an NZr component wave in each block.